1. Materials Research and Education Center Department of Mechanical Engineering Auburn University Auburn AL 36849 USA
2. Department of Electrical Engineering & Computer Sciences Massachusetts Institute of Technology Cambridge MA 02139 USA
3. John A. Paulson School of Engineering and Applied Sciences Harvard University Cambridge MA 02139 USA
4. Department of Physics Massachusetts Institute of Technology Cambridge MA 02139 USA
5. Sichuan University Pittsburgh Institute Sichuan University Sichuan Chengdu 610017 China
6. Department of Physics University of California, San Diego La Jolla CA 92093 USA
7. School of Electrical and Electronic Engineering Nanyang Technology University 50 Nanyang Avenue Singapore 639798 Singapore
8. Department of Physics Columbia University New York NY 10027 USA